Immune checkpoint inhibitors (ICIs) such as anti-programmed cell death protein 1 (PD-1)/programmed death-ligand 1 (PD-L1) and anti-cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) antibodies have revolutionized treatment for immunologically “hot” tumors including melanoma and have led to long-term survival for a subset of patients. The gene discussed is PDCD1; the disease is melanoma.